Investigation on nitrogen distribution and corrosion resistance of 35CrMoA steel in laser quenching-nitriding

Laser quenching and nitriding treatment had been performed on 35CrMoA steel,and the microstructure,phase,nitrogen distribution and corrosion resistance of laser quenching/nitrided layer were investigated by means of SEM,XRD,EPMA,and compared with the gas nitrided layers.The results show that the content of ε-Fe₃N is higher in the laser quenching/nitrided layer while the content of the brittle ζ-Fe₂N is lower than that of the gas nitrided layer.The density of N in the surface is lower compared with that of the gas nitrided layers,and the density of N in the surface of laser quenching/nitrided layer declines slowly while drops sharply in the gas nitrided layers.By laser quenching,grain size becomes small,and dislocations increase,which make the bidirectional dissolution rate of γ' phase be faster than the hydrogen storage rate of ε phase,and ε and γ' phase's hindrance on diffusion is faded,with the results that the thickness of compound layer decreases,and the thickness of nitrided layer increases.Ecorr of laser quenching/nitriding layer was improved comparing with gas nitriding while Icorr decreases from 57.68 μA/cm² of gas nitriding layer to 3.166 μA/cm² of composite nitriding layer.As a result,its corrosion resistance was improved significantly.